Microcapsules having walls of polyaddition products of water-insoluble polyamines with water-soluble polyisocyanate adducts

ABSTRACT

Microcapsules having a hydrophobic core material and capsule walls formed by the reaction of water-insoluble polyamines with water-soluble bisulphite adducts of polyisocyanates, a process for the production thereof which is characterized in that a mixture of a hydrophobic core material and water-insoluble polyamines is emulsified in water or in an aqueous protective colloid solution to the required particle size, water-soluble bisulphite adducts of polyisocyanates in the form of powders or aqueous solutions are added and the mixture is left to react to completion at temperatures of from 1° to 140° C., and applications thereof.

This is a continuation of application Ser. No. 506,451, filed June 21,1983, now U.S. Pat. No. 4,517,141, issued May 14, 1985.

Microcapsules have been produced by dispersing in water solutions ofsubstances to be encapsulated (core material) and polyisocyanates inhydrophobic solvents, adding to the continuous aqueous phase a polyaminewhich is soluble therein and producing a polyurea at the interface ofthe dispersed droplets of polyisocyanate and polyamine. This method ofmicroencapsulation by interfacial polyaddition may only be applied ifthe core material is inert towards polyisocyanates and if awater-soluble polyamine may be used. It cannot be used for encapsulatingsubstances which react with polyisocyanates, for example polyaminesthemselves. Water-insoluble polyamines are also unsuitable for thismethod.

The present invention relates to microcapsules having a hydrophobic coreand capsule walls formed by the reaction of water-soluble polyisocyanateadducts with water-insoluble polyamines. The present invention alsorelates to a process for producing microcapsules which is characterisedin that a mixture of a hydrophobic core material and water-insolublepolyamines in water or an aqueous protective colloid solution isemulsified to the required particle size, water-soluble bisulphiteadducts of polyisocyanates are added in the form of powders or aqueoussolutions and the mixture is left to react to completion at temperaturesof from 1° to 140° C. The core material according to the presentinvention may consist of the wall-forming polyamine alone or mayadditionally contain a solvent or an active substance or both. If thecore material contains only polyamine, only part of the polyamine isused for forming the wall of the capsule so that the capsule alsocontains polyamine. If the core material contains solvent and/or activesubstance in addition to polyamine, the polyamine may be completely usedfor forming the capsule wall, so that the capsules contain an activesubstance, a solvent or both. Depending on the contents thereof, themicrocapsules may be used, for example, as dye-precursor-containingmicrocapsules in reaction copying papers, as microcapsules containingflameproofing agents or blowing agents or catalysts in the production ofpolymers or as solvent-containing microcapsules in the reactivation ofadhesives and also as dye- or pigment-containing microcapsules as tonersin copying systems and also as active carbon-containing microcapsulesfor use in absorbing systems of all types.

The diameter of the capsules may be from 0.2 to more than 2000 μm,preferably up to 2000 μm. Where the capsules are used asdye-precursor-containing capsules for reaction copying papers, capsuledistributions having median values of from 3 to 10 μm are preferred.Where relatively small capsules are present in the form of agglomeratesor clusters, corresponding distributions of the agglomerates with mediandiameter values of from 3 to 10 μm are preferred.

In the case of encapsulated reaction components or catalysts, the mediancapsule diameter values are preferably from 3 to 20 μm, because, forexample, it is only with diameters distributed over this range that itis possible to obtain sufficiently uniform dispersion of the activesubstances in the capsules reacting to completion.

For specialised applications, it may even be advantageous to use largercapsules, particularly when the active substances have to be releasedover large areas or in their entirety by mechanical destruction of thecapsule walls, for example during extrusion or mixing under high shearforces or, for example, in the case of dried, reactivatable adhesivelayers incorporating microencapsulated solvents which dissolve andreactivate the adhesives by destruction of the capsule walls by theapplication of pressure. For such systems, capsule diameters of from 100to 1000 μm are preferred, capsule diameters of from 300 to 500 μm beingparticularly preferred.

The percentage of the active substance-containing microcapsulesconstituted by the walls may vary widely. Depending on the applicationenvisaged, higher percentages of the capsules will be constituted by thewalls, for example in cases where the capsules are required to beparticularly impervious or in cases where mixtures containingmicrocapsules for the production of mouldings are required to show highstorage stability. Alternatively, lower percentages of the capsules willbe constituted by the walls in cases where, for example in the event ofmechanical destruction of the capsules, the pressure required for thecontents of the capsules to be completely released cannot or must notexceed certain levels.

An increase in the stability of the capsules was observed with anincrease of from 9 to 50% in the percentage of the capsules constitutedby the walls. Although higher percentages of the capsules may inprinciple be constituted by the walls, this is generally not desirable.The microcapsules according to the present invention are produced byemulsifying a mixture of water-insoluble substances and water-insolublepolyamines in water or, optionally, in an aqueous protective colloidsolution to required particle size, adding water-soluble bisulphiteadducts of polyisocyanates in the form of powders or aqueous solutionsand subsequently carrying out the reaction at temperatures of from 1° to140° C.

The protective colloid is present in the aqueous phase in smallquantities, preferably in a concentration of from 0.01 to 2%, moreparticularly 0.25% by wt. Additional thickeners acting as stabilisersagainst sedimentation may optionally be present in the same quantitiesas the protective colloid. However, it is pointed out in this connectionthat protective colloids which prevent droplets from recombining duringemulsification and the microcapsules formed from agglomerating andthickeners which act as stabilisers against sedimentation cannot beclearly defined in regard to the range within which they act. Protectivecolloids always develop a certain sedimentation-stabilising effect,while in many cases, thickeners also show a distinct protective colloideffect. Suitable protective colloids are, for example, polyvinylalcohol, carboxy methyl cellulose and gum arabic. Suitable thickenersare, for example, alginates and xanthans.

The oil phase of the oil-in-water emulsion may amount to from 0.5 to50%, by weight, preferably from 15 to 45%, by weight, more preferablyfrom 30 to 40%, by weight.

The emulsion is prepared by introducing a mixture of the water-insolublesubstance and the polyamine or the polyamine mixture in liquid or moltenform with stirring into the optionally heated receiving medium.

If the mixture of water-insoluble substances and polyamine has a meltingpoint above room temperature, the emulsification process may be dividedinto a forming step, for example by spraying from the melt or bygrinding, and a dispersing step in which the finely divided material isdispersed in the aqueous receiving medium. To form the capsule walls,the reacting polyamine has to be heated to its melting point.

Emulsification may be carried out using conventional commercialapparatus, such as laboratory stirrers, propeller stirrers or mixingunits operating on the rotor-stator principle, such as mixing sirens. Itis not so much the intense shear effect which is important foremulsification as thorough intermixing. It is typical of the amines usedin accordance with the present invention that they may be emulsifiedvery easily even in admixture with other water-insoluble substances. Insmall vessels, vigorous shaking is often sufficient to produce anemulsion (surfactant effect of water-insoluble polyamines).

If the bisulphite adducts of polyisocyanates are to be added in the formof aqueous solutions, the concentration thereof generally amounts tofrom 0.5 to 80%, by weight, preferably from 10 to 60%, by weight, morepreferably from 20 to 45%, by weight.

The oil phase of the emulsion must contain at least that quantity ofpolyamine which is necessary for encapsulation. Based on the polyamine,bisulphite adduct is added in such a quantity that the required wallcomponent is obtained from the reaction of the polyamine with the maskedpolyisocyanate, the NH₂ -groups of the amine being expected to reactwith the (masked) NCO-groups of the polyisocyanate in a molar ratio of1:1.

If the polyamine is to react completely, the bisulphite adduct must beused in the corresponding stoichiometric quantity. To acceleratecomplete reaction of the amine, it is advisable to use the bisulphiteadduct in a quantity from 5 to 20% higher than the stoichiometricquantity.

If a portion of the polyamine is to remain in the capsule core,correspondingly less bisulphite adduct should be used taking intoaccount the required percentage wall component.

Preferred percentage wall components are from 5 to 64%, by weight,preferably from 8 to 40%, by weight, more preferably from 10 to 12%, byweight. The reaction of the components for forming the walls of thecapsules takes place at temperatures of from 1° to 140° C.

In the case of bisulphite adducts of aromatic polyisocyanates,temperatures of from 1° to 100° C. are preferred, temperatures from 20°to 40° C. being particularly preferred.

In the case of bisulphite adducts of aliphatic po-yisocyanates,temperatures of from 50° to 140° C. are preferred, temperatures from 70°to 98° C. being particularly preferred.

Increasingly more rapid, spontaneous (in the absence of amine)resplitting of the bisulphite adducts takes place with increasingtemperature. If solutions of bisulphite adducts are heated before mixingwith the polyamine emulsion, the solution should only be at elevatedtemperatures for a limited period. The times and temperatures during andat which approximately 5% of two bisulphite adducts are resplit areshown in Table I.

                  TABLE I                                                         ______________________________________                                                   Adduct according                                                                           Adduct according                                      T          to Example 2 to Example 12                                         ______________________________________                                         20° C.                                                                           unlimited    2        hours                                         50° C.                                                                           50      hours    30     minutes                                     80° C.                                                                           10      hours    8      minutes                                    100° C.                                                                           120     minutes  1      minute                                     120° C.                                                                           30      minutes  10     seconds                                    130° C.                                                                           8       minutes  --                                                140° C.                                                                           2       minutes  --                                                ______________________________________                                    

The polyamines used for forming the capsule walls are insoluble inwater. In the context of the present invention, water-insolublepolyamines are to be understood to be polyamines of which less than 2%,preferably less than 1% o, dissolves in the aqueous phase. Polyaminesare to be understood to be amines which contain at least two primaryamino groups. Polyamines having melting points above room temperatureare dissolved, optionally at elevated temperature, or heated to a commonmelting point in the water-insoluble substance to be encapsulated.Emulsification should take place in heated water above the commondissolving or melting temperature, optionally under excess pressure ifthe dissolving or melting temperature is in the vicinity of or above theboiling temperature of the water.

Diamines are preferably used as the polyamine.

Aliphatic diamines suitable for use in accordance with the presentinvention are, for example, 1,11-undecamethylene diamine,1,12-dodecamethylene diamine and also mixtures and isomers thereof,perhydro-2,4'- and -4,4'-diaminodiphenyl methane, p-xylylene diamine,diaminoperhydro-anthracenes (DE-OS No. 2,638,731). It is also possiblein accordance with the present invention to use acid dihydrazides, forexample oxalic acid dihydrazide, the dihydrazides of malonic acid,succinic acid, glutaric acid, adipic acid, β-methyl adipic acid, sebacicacid and terephthalic acid.

Examples of aromatic diamines are the bis-anthranilic acid estersaccording to DE-OS Nos. 2,040,644 and 2,160,590, the 3,5- and2,4-diaminobenzoic acid esters according to DE-OS No. 2,025,900, thediamines containing ester groups described in DE-OS Nos. 1,803,635 (U.S.Pat. Nos. 3,681,290 and 3,736,350), 2,040,650 and 2,160,589, thediamines containing ether groups according to DE-OS Nos. 1,770,525 and1,809,172 (U.S. Pat. Nos. 3,654,364 and 3,736,295),2-halogen-1,3-phenylene diamines optionally substituted in the5-position (DE-OS Nos. 2,001,772; 2,025,896 and 2,065,869),3,3'-dichloro-4,4'-diaminodiphenyl-methane,4,4'-diaminodiphenyl-methane, 4,4'-diaminodiphenyl-disulphides (DE-OSNo. 2,404,976), diaminodiphenyl dithioethers (DE-OS No. 2,509,404),aromatic diamines substituted by alkylthio groups (DE-OS No. 2,638,760)and the water-insoluble high-melting diamines mentioned in DE-OS No.2,635,400. Ethylene glycol-bis-(p-aminobenzoic acid ester),2,2'-diaminoazobenzene, 3,3'-diaminoazobenzene, 4,4'-diaminoazobenzene,2,3-diaminobenzoic acid, 2,5-diaminobenzoic acid,2,2'-diaminobenzophenone, 4,4'-diaminobenzophenone,4,4'-diaminostilbene, 2,2'-diaminostilbene,4,4'-diaminotriphenylmethane, 1,5-naphthylene diamine, 2,6-naphthylenediamine, 2,7-naphthylene diamine, 1,2-diaminoanthraquinone,1,5-diaminoanthraquinone, 1,4-diaminoanthraquinone,2,6-diaminoanthraquinone, 3,6-diaminoacridine, 4,5-diaminoacenaphthene,4,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl sulphone,3,3'-dimethoxy-benzidine, 4,4'-diaminodiphenyl sulphone,2,3-diaminofluorine, 2,5-diaminofluorine, 2,7-diaminofluorine,9,10-diaminophenanthrene, 3,6-diaminodurol,p-xylylene-bis-(o-aminothiophenyl) ether,4,3'-diamino-4'-chlorobenzanilide, 4,2'-diamino-4'-chlorobenzanilide,4-chloro-3,5-diaminobenzoic acid ethyl ester, 4-chloro-3-aminobenzoicacid-(4-chloro-3-aminophenyl ester), 4-chloro-3-aminobenzoicacid-(3-chloro-4-aminophenyl ester), 4-aminobenzoicacid-(3-chloro-4-aminophenyl ester), succinic aciddi-(3-chloro-4-amino)-phenyl ester, ethyleneglycol-bis-(4-chloro-3-amino)-benzoic acid ester,3,3'-dichloro-4,4'-diaminodiphenyl carbonate,4,4'-dichloro-3,3'-diaminodiphenyl carbonate,4-methyl-3,5-diaminobenzoic acid ethyl ester, 3,5-diaminobenzoic acidmethyl ester and 4,4'-diaminodiphenyl-methane-3,3'-dicarboxylic aciddimethyl ester.

Examples of aliphatic-aromatic diamines are the aminoalkyl thioanilinesaccording to DE-OS No. 2,734,574.

The following are additional diamines which are particularly preferredfor the purposes of the present invention:

Aliphatic diamines

trans, trans-4,4'-diaminodicyclohexyl-methane; diaminomethylatedcyclododecane; bis-(6-amino-n-hexyl carbamic acid)-dipropylene glycoldiester.

Aromatic diamines

diethyl tolylene diamine;3,5-diethyl-3',5'-diisopropyl-4,4'-diaminodiphenyl-methane;3,3',5,5'-tetraisopropyl-4,4'-diaminodiphenyl-methane;3,3',5,5'-tetraethyl-4,4'-diaminodiphenyl-methane and mixtures thereof;diphenylmethane-3,3'-dithiomethyl-4,4'-diamine;3,3'-carboxyethyl-4,4'-diaminodiphenyl-methane; dichlorinated1,3-phenylene diamines; triisopropylated 1,3-phenylene diamine;3,5-diamino-4-chlorobenzoic acid isobutyl ester;3,5-diamino-4-methyl-benzoic acid isobutyl ester; bis-(4-aminobenzoicacid)-1,3-propane diol diester; bis-(4-aminobenzoicacid)-1,3-(2-ethyl)-propane diol diester; and naphthylene-1,5-diamine.

The core materials used in addition to polyamines are alsowater-insoluble and show the insolubility in water mentioned above inrespect of the polyamines. The core materials to be encapsulated must beinert towards primary amino groups. The wall-forming polyamine must bemiscible with the core material where it is in the form of a liquid ormelt. The polyamine may itself form part of the capsule interiortogether with other core materials. Furthermore, finely disperse solidsmay be present in dispersion in the capsule core.

The following water-insoluble substances may be used: variouswater-miscible solvents which dissolve dye-precursors suitable forcopying papers. Examples are chlorinated diphenyls, dodecyl benzene,mixtures of partially hydrogenated and non-hydrogenated terphenylene,isopropyl diphenyl, diisopropyl benzene, benzoic acid ethyl esters,mixtures of diphenyl and diphenyl ethers, phthalic acid dibutyl ester,aralkyl or diaryl ethers, xylenes or conventional commercial mixtures ofaromatics of the type accumulating in the aromatisation plants of thepetrochemical and petroleum industries; also chlorinated paraffins,cottonseed oil, peanut oil, silicone oil, tricresyl phosphate,monochlorobenzene, alkylated diphenyls, alkylated naphthalenes andrelatively highly alkylated benzenes.

In many cases diluents, such as kerosene, n-paraffins and isoparaffins,are added to the solvents. The diluents may be encapsulated bothseparately and also in admixture with the above-mentioned solvents.

Solutions of dye precursors in the above-mentioned solvents, so-calledcolour-forming solutions, may advantageously be encapsulated by theprocesses mentioned above.

Examples of dye-precursors are triphenyl methane compounds, diphenylmethane compounds, xanthene compounds, thiazine compounds and spiropyrancompounds.

Particularly suitable dye-precursors are triphenyl methane compounds:3,3-bis-(p-dimethylaminophenyl)-6-dimethylaminophthalide and3,3-bis-(p-dimethylaminophenyl)-phthalide ("malachite green lactone");diphenyl methane compounds: 4,4'-bis-dimethylaminobenzhydrilbenzylether, N-halogen phenyl leucolamine, N-β-naphthyl leucolamine,N-2,4,5-trichlorophenyl leucolamine, N-2,4-dichlorophenyl leucolamine;xanthene compounds: rhodamine-β-anilinolactam,rhodamine-β-(p-nitroaniline)-lactam,rhodamine-β-(p-chloroaniline)-lactam,7-dimethylamino-2-methoxy-fluorane, 7-diethylamino-3-methoxy-fluorane,7-diethylamino-3-methyl-fluorane, 7-diethylamino-3-chloro-fluorane,7-diethylamino-3-chloro-2-methyl-fluorane,7-diethylamino-2,4-dimethyl-fluorane,7-diethylamino-2,3-dimethyl-fluorane,7-diethylamino-(3-acetylmethylamino)-fluorane,7-diethylamino-3-methyl-fluorane, 3,7-diethylamino-fluorane,7-diethylamino-3-(dibenzylamino)-fluorane,7-diethylamino-3-(methylbenzylamino)-fluorane,7-diethylamino-3-(chloroethylmethylamino)-fluorane,7-diethylamino-3-(dichloroethylamino)-fluorane,7-diethylamino-3-(diethylamino)-fluorane; thiazine compounds: N-benzoylleucomethylene blue, o-chlorobenzoyl leucomethylene blue, p-nitrobenzoylleucomethylene blue; spiro compounds:3-methyl-2,2'-spiro-bis-(benzo(f)-chromene).

It is also possible to encapsulate low-boiling liquids of the typesuitable for use as blowing agents, such as methylene chloride,chloroform or "Frigen"; water-insoluble alcohols, water-insolublecatalysts, particularly those containing secondary or tertiary aminogroups, water-insolub-e, sluggishly reacting monoamines; water bound inwater-insoluble hydrates of the type formed by numerous water-insolublepolyamines; finely divided solids dispersed in liquid or moltenpolyamine and/or solvents. Such solids may be water-insoluble minerals,metal oxides or metals, such as quartz, chalk, bauxite, iron oxides,nickel, copper, inorganic pigments or other organic solids, such asactive carbon or organic pigments. The polyamines used for forming thecapsule walls may also be used as the material to be encapsulated. Inthis case, generally from 5 to 64%, by weight, preferably from 8 to 40%,by weight, of the polyamine is used for forming the capsule walls, theremainder being left as the capsule filling.

Before emulsification in the aqueous phase, the substances to beencapsulated are mixed with the polyamines in the conventional mannerand then emulsified together in the aqueous phase.

The percentage of polyamine in the disperse phase before formation ofthe capsule walls generally amounts to from 1 to 95%, by weight,preferably from 3 to 50%, by weight, more preferably from 5 to 13%, byweight.

The polyisocyanate bisulphite adducts used are soluble in water, inother words they form a clear solution in water containing from 0.5 to80 g, preferably from 20 to 40 g, of bisulphite adduct per 100 ml. Thepolyisocyanates are aliphatic or aromatic and contain at least twoisocyanate groups.

Various known aliphatic and aromatic polyisocyantes may be used as thebisulphite adducts providing they are sufficiently soluble in water. Inaddition to the pure products, it is also possible to use mixtures ofbisulphite adducts of various isocyanates and also bisulphite adducts ofpolyisocyanate mixtures. The polyisocyanates in the mixtures may containvarying numbers of isocyanate groups, bifunctional and trifunctionalmolecules being typical. While the bisulphite adducts of the aliphaticpolyisocyanates are used in the form of aqueous solutions or powders, itis preferred in the case of bisulphite adducts of aromaticpolyisocyanates to produce a powder which is dissolved in the slurryimmediately before formation of the microcapsule. In general, it doesnot matter which cation of the bisulphite adduct is selected, sodium,potassium and ammonium ions being the norm. In borderline cases ofsolubility in water, the bisulphite adduct selected will be the adducthaving the best solubility in water, generally the sodium salt.

Preferred water-soluble bisulphite adducts are the readily obtainableadducts of aliphatic polyisocyanates. They may be used in powder form orin the form of aqueous solutions.

Resplitting of the bisulphite adducts with aliphatic polyisocyanatesonly occurs to a significant extent at elevated temperatures. Capsuleformation is considerably accelerated by heating the slurry to from 50°to 90° C. In general, stable microcapsules are formed in a sufficientlyshort time at such temperatures. For microencapsulation on an industrialscale, particularly in cases where it is carried out continuously, it ispreferred to work under excess pressure at temperatures above 100° C. inorder correspondingly to accelerate the encapsulation process.Water-soluble bisulphite adducts of aromatic polyisocyanates may also beused. Capsule formation takes place sufficient-y quickly at temperaturesas low as room temperature so that there is generally no need for areaction at elevated temperatures. At very high temperatures, capsuleformation may even be disrupted by agglomeration of the microcapsules orby the precipitation of polyurethane urea outside the capsule walls.

The adducts of the aromatic polyisocyanates do not have the samestability in water as those of the aliphatic polyisocyanates. Attemperatures above room temperature, resplitting into disulphite andpolyisocyanate very soon takes place as the temperature increases withcorresponding conversion of the isocyanate groups by reaction with waterto form polyurethane urea. Accordingly, such adducts are preferablyadded to the slurry in the form of a dry powder just before thereaction. Although there are distinct advantages with regard to the wallforming temperature for microcapsules, the bisulphite adducts ofaromatic polyisocyanates are less preferred than those of aliphaticpolyisocyanates. The reasons for this lie in the poorer safety of theprocess during microencapsulation and in the fact that this group ofadducts is more difficult to produce on a commercial scale.

The following aromatic or aliphatic polyisocyanates which are soluble inwater in the form of the bisulphite adducts thereof are mentioned by wayof example:

Starting components are aliphatic, cycloaliphatic, araliphatic, aromaticand heterocyclic polyisocyanates of the type described, for example, byW. Siefken in Justus Liebigs Annalen der Chemie, 562, pages 75 to 136,for example those corresponding to the following general formula:

    Q (NCO).sub.n

wherein

n=2-4, preferably 2; and

Q represents an aliphatic hydrocarbon radical containing from 2 to 18,preferably from 6 to 10, carbon atoms, a cycloaliphatic hydrocarbonradical containing from 4 to 5, preferably from 5 to 10, carbon atoms,an aromatic hydrocarbon radical containing from 6 to 15, preferably from6 to 13, carbon atoms or an araliphatic hydrocarbon radical containingfrom 8 to 15, preferably from 8 to 3, carbon atoms, for example ethylenediisocyanate, 1,4-tetramethylene diisocyanate, 1,6-hexamethylenediisocyanate, 1,12-dodecane diisocyanate, cyclobutane-1,3-diisocyanate,cyclohexane-1,3- and -1,4-diisocyanate and mixtures of these isomers,1-isocyanato-3,3,5-trimethyl-5-isocyanatomethyl cyclohexane (DE-AS No.1,220,785, U.S. Pat. No. 3,401,190), 2,4- and 2,6-hexahydrotolylenediisocyanate and mixtures of these isomers, hexahydro-1,3- and/or-1,4-phenylene diisocyanate, perhydro-2,4'- and/or -4,4'-diphenylmethanediisocyanate, 1,3- and 1,4-phenylene diisocyanate, 2,4- and 2,6-tolylenediisocyanate and mixtures of these isomers, diphenyl methane-2,4'-and/or -4,4'-diisocyanate and naphthylene-1,5-diisocyanate.

According to the present invention, it is also possible to use, forexample, triphenylmethane-4,4',4"-triisocyanate,polyphenyl-polymethylene polyisocyanates of the type obtained byphosgenating aniline/formaldehyde condensates and described, forexample, in British Pat. Nos. 874,430 and 848,671, m- andp-isocyanatophenyl sulphonyl isocyanates according to U.S. Pat. No.3,454,606, perchlorinated aryl polyisocyanates of the type described,for example, in DE-AS No. 1,157,601 (U.S. Pat. No. 3,277,138),norbornane diisocyanates according to U.S. Pat. No. 3,492,330,polyisocyanates containing allophanate groups of the type described, forexample, in British Pat. No. 994,890, in Belgian Pat. No. 761,626 and inNL Patent Application No. 71 02 524, polyisocyanates containingisocyanurate groups of the type described, for example, in U.S. Pat. No.3,001,973, in German Pat. Nos. 1,022,789; 1,222,067 and 1,027,394 and inDE-OS Nos. 1,929,034 and 2,004,048, polyisocyanates containing urethanegroups of the type described, for example, in Belgian Pat. No. 752,261or in U.S. Pat. Nos. 3,394,164 and 3,644,457 polyisocyanates containingacylated urea groups according to German Pat. No. 1,230,778,polyisocyanates containing biuret groups of the type described, forexample in U.S. Pat. Nos. 3,124,605; 3,201,372 and 3,124,605 and inBritish Pat. No. 889,050. Mixtures of the above-mentionedpolyisocyanates may also be used.

Particularly preferred polyisocyanates are 1,6-hexamethylenediisocyanate,1-isocyanato-3,3,5-trimethyl-5-isocyanatomethyl-cyclohexane, 2,4- and2,6-tolylene diisocyanate, diphenyl-methane-2,4- and/or-4,4'-diisocyanate and also polyisocyanates containing urethane,allophanate, isocyanurate, urea or biuret groups and/or oxadiazinetrione groups derived from the diisocyanates mentioned above.

Bisulphite adducts of aliphatic polyisocyanates are completely stable inwater, but are converted into polyureas by reaction with primary aminogroups. The reaction in question taken place at the interface betweenthe outer aqueous phase and the disperse amine phase. The polyisocyanateis incorporated into the capsule wall at the interface by polymerformation while the bisulphite remains behind in the aqueous phase.

Bisulphite adducts of polyisocyanates, i.e. reaction products of sodiumhydrogen sulphite with ailphatic and aromatic polyisocyanates are knownand are described, for example, by S. Petersen in Liebig's Annalen derChemie, Vol. 562 (1949), pages 205 et seq. The reaction thereof withamines in the aqueous phase to form polyureas is also known.

In spite of this, it was extremely surprising and unexpected to thoseskilled in the art to find that the described microencapsulation processcould be carried out so easily. This is because those skilled in the artwould have expected bisulphite adducts of polyisocyanates to react withwater during resplitting in view of the very fine dispersion of themolecules in the aqueous solution and the amines formed to react furtherwith other bisulphite adducts to form ureas. In the case of bisulphiteadducts of aromatic polyisocyanates, this latter reaction is known asspontaneous resplitting at room temperature. In addition, those skilledin the art would have expected minimal solubility (a few ppm) of thepolyamine in water to be sufficient to split the finely dispersedbisulphite adducts in the solution and, as a result, to causepolyurethane ureas to be formed by precipitation outside the capsulewall. This preconception was in fact initially confirmed in testscarried out using bisulphite adducts produced in the conventional way tothe extent that capsules were not formed in the manner according to thepresent invention or, after initial formation, agglomerated in theslurry on stirring, causing the slurry to gel to a very considerableextent. In no case was it possible to isolate the capsules, for exampleby spray drying.

It was only when a powder-form bisulphite adduct which had beensubjected to a particular purification process was used that it wasrealised that all the hitherto used aqueous solutions of the bisulphiteadducts contained small quantities of emulsifier from the productionprocess. Following removal of the emulsifier, it was possible to producemicrocapsules in the manner according to the present invention even withaqueous solutions.

Solutions of bisulphite adducts may still contain bisulphites from theproduction process. It is preferred to convert these bisulphite residuesinto neutral salts before the beginning of the encapsulation process bythe addition of appropriate quantities of neutralising substances, suchas hydroxides, carbonates and/or bicarbonates.

The process by which the capsule wall is formed may be accelerated andpromoted by other measures, for example by the addition of catalystswhich promote resplitting of the bisulphite adducts, such as triethylenediamine and diethanolamine, or by conversion of the acid bisulphitesnewly formed into neutral salts by the addition of appropriatequantities of hydroxide, carbonates and/or bicarbonates.

This addition has to be gauged very carefully commensurate with theprogress of formation of the capsule wall. If the addition is made allat once or in an excessive quantity, more polyisocyanate is easilyreleased than may be directly reacted with the polyamine, resulting inmore or less pronounced agglomeration.

If the resplitting catalyst, for example diethanolamine, is introducedinto the oil phase before emulsification, it always acts in the vicinityof the interface on passing over from the disperse phase into the outerphase. Agglomeration may thus be avoided.

The encapsulation process according to the present invention and themicrocapsules obtained have a number of advantages.

By virtue of its range of variation, the process according to thepresent invention frequently enables more favourable or cost-reducingparameters to be selected. Thus, where microencapsulation is carried outusing high-melting polyamines, it may be advantageous to use a mixtureof polyamines. In general, a polyamine which is liquid at roomtemperature dissolves solid higher-melting amines so that encapsulationmay be carried out at a relatively low temperature. This has aparticularly cost-reducing and technically simplifying effect, forexample, when encapsulation under excess pressure may be avoided in thisway.

The microcapsules produced by the described process are used in the formof a dispersion in water, although they may also be converted byspray-drying into powders. This may be done using conventional technicalequipment and does not call for specialised measures. In addition to thesolid constituents of the protective colloids, the powders obtained byspray drying also contain the bisulphites split off or salts formedtherefrom by further reaction.

The quantity of salts formed may amount to as much as 20% of the drymatter, depending on the wall thickness adjusted. In general, thepresence of the salts does not present problems. In certain cases,however, the salts have to be removed from the spray-dried product, i.e.the powder. Since the salt crystals which accumulate during spray dryingare considerably smaller than the microcapsules, the removal thereof mayreadily be obtained in the course of the spray drying process, forexample by correspondingly designing and arranging the cyclone andfollowing tube filter.

The microcapsules according to the present invention may be used, forexample, in the following fields:

As capsules containing dye-precursors for the production of reactioncopying papers, as additives in the production of mouldings from resins,elastomers, foams, for example in the form of encapsulatedflame-proofing agents, for example based on organic phosphorus orchlorine and bromine compounds, or blowing agents or in the form ofencapsulated catalysts, particularly containing secondary or tertiaryamino groups; as solvent capsules in the reactivation of adhesivelayers; as dye- or pigment-containing capsules used in powder form astoners for copying systems; as active carbon-containing capsules forabsorbing systems of all types, for example for incorporation inprotective clothing or for dialysis systems.

In cases where the capsules contain only polyamines, they may be used asdelayed-action cross-linkers for polyurethane systems.

The present invention is illustrated by the following Examples: Allpercentage and parts indicated are by weight.

Reverse Encapsulation EXAMPLE 1 (a) Preparation of a protective colloidsolution

A protective colloid solution is prepared from 1 part of polyvinylalcohol (Mowiol 26/88, a product of Hoechst AG, Frankfurt), 2 parts ofxanthan (Kelzan D, a product of the Kelco Division of BaltimoreAircoil/Chemviron SA) and 397 parts of distilled water by stirring atroom temperature.

(b) Preparation of a colour-former solution

46 parts of benzoyl leucomethylene blue and 139 parts of crystal violetlactone are dissolved in 3932 parts of diisopropyl naphthalene byheating and stirring and 983 parts of isohexadecane are added to theresulting solution.

(c) Preparation of a colour-former solution

1 part of a green-developing fluorane derivative (Pergascript Olive IG,a product of Ciba-Geigy) is dissolved in 19 parts of diisopropyldiphenyl by stirring and heating to 80° C.

EXAMPLE 2

270 g of a protective colloid solution corresponding to Example 1(a) areintroduced at room temperature into a glass beaker, followed by theaddition with stirring (at 950 r.p.m. using a Kotthoff type MS 1 FCABmixing siren, a product of the Kotthoff company of Rodenkirchen/Cologne)at room temperature of 55 g of the colour-former solution of Example1(b) and 9.5 g of diethyl tolylene diamine. The rotational speed is thenincreased to 9000 r.p.m. for 45 seconds, resulting in the formation of avery fine oil-in-water emulsion. The rotational speed is reduced to 950r.p.m. for 15 seconds, followed by the addition of 200 g of a clearsolution (temperature 20° C.) of 180 g of protective colloid solutionand 20 g of a powder-form sodium bisulphite adduct of hexamethylenediisocyanate.

After a second emulsification phase lasting 45 seconds with the mixingsiren rotating at 9000 r.p.m., the slurry is transferred to a beakerequipped with a reflux condenser and laboratory stirrer and stirred at200 r.p.m. for a total of 450 minutes while heating to 90° C.

An agglomerate-free slurry containing smooth, round and clearlytransparent capsules ranging from 1 to 16 μm in diameter is obtained.Spray drying using a laboratory spray dryer (a Buchi 190 Mini SprayDryer, a procut of the Buchi company of CH-9230 Flawil, Switzerland)gives a white, substantially agglomerate-free capsule powder. Thecapsules have diameters in the same range as the slurry and a liquidcore.

EXAMPLE 2(a)

To produce a carbonless copying set, the slurry prepared in accordancewith Example 2 is knife-coated in a layer thickness of 20 μm onto asheet of typing paper. After the aqueous constituents of the slurry havedried in air at room temperature, a CB (coated back) sheet (donor sheet)is obtained and is placed with its coated back on the clay-coated frontof a conventional commercial CF (coated front) sheet (receiving sheet).

When the top of the CB-sheet is written on with a ballpoint pen, thecapsules of the CB-layer burst, releasing the colour-former solution,and the dissolved dye-precursor reacts in the CF-sheet to form a darkblue dye. A correspondingly dark blue coloured copy is obtained on thetop of the receiving sheet.

EXAMPLE 3(a)

The procedure is as in Example 2. In addition, 15 g of a 30% NaOHsolution are added 5 minutes after the beginning of the test.

Thereafter, capsule formation takes place very much more quickly than inExample 2 (i.e. in 10 minutes), but is accompanied by a marked tendencyof the capsules to agglomerate. The test is terminated after a total of60 minutes. The slurry obtained contains almost completely agglomeratedcapsules. Most of the agglomerates may be broken down into individualcapsules. The individual capsules have diameters of from 1 to 15 μm anda wrinkled surface and are non-spherical and opaque.

EXAMPLE 3(b)

The procedure is as in Example 2. In addition, 5.6 g of Na₂ CO₃ powderare added 5 minutes after the beginning of the test. Thereafter, capsuleformation takes place in 15 minutes, accompanied by the formation ofclusters of agglomerates having diameters of up to 60 μm. The test isterminated after a total of 60 minutes. The agglomerates may readily benon-destructively broken down into individual capsules on a specimenholder. The individual capsules have diameters of from 1 to 10 μm andare round, transparent and have smooth surfaces. High-qualitycoated-back copying paper may be produced by wet coating as in Example2(a).

EXAMPLE 3(c)

The procedure is as in Example 2. In addition, 8.9 g of NaHCO₃ powderare added 5 minutes after the beginning of the test. Thereafter, capsuleformation takes place in 10 minutes accompanied by the formation ofrelatively loose agglomerates up to 230 μm in diameter. The test isterminated after a total of 55 minutes. To break down the agglomerates,the slurry is returned to the mixing siren and stirred for 5 minutes at3000 r.p.m. Thereafter, a substantially agglomerate-free slurry isobtained, containing round, transparent capsules having a smooth surfaceand diameters of from 1 to 14 μm.

High-quality CB-copying papers may be produced by wet coating as inExample 2(a).

EXAMPLE 3(d)

The procedure is as in Example 2. In addition, 15.8 g of triethanolamineare added 15 minutes after the beginning of the test. Thereafter,capsule formation takes place in 10 minutes accompanied by the formationof agglomerates up to 32 μm in diameter. The test is terminated after 85minutes. To break down the agglomerates, the slurry is returned to themixing siren and stirred at 3000 r.p.m. for 3 minutes. Thereafter, theslurry contains round, transparent capsules having a smooth surface anddiameters of from 1 to 11 μm. Approximately 30% of the mainly relativelysmall capsules form agglomerates up to 18 μm in diameter.

High-quality CB-copying papers may be produced by wet coating in thesame way as in Example 2(a).

Spray-drying gives a capsule powder containing approximately 50% ofindividual capsules from 1 to 11 μm in diameter and agglomerates up to36 μm in diameter. Redispersion of the capsule powder in a 2% polyvinylalcohol solution (Mowiol 26/88, a product of Hoechst AG, Frankfurt)gives a coating blend from which high quality CB copying papers may beproduced by wet coating in the same way as in Example 2(a).

EXAMPLE 4

250 g of a protective colloid solution corresponding to Example 1(a) areintroduced at room temperature into a glass beaker, followed by theaddition with stirring (Kothoff mixing siren, 950 r.p.m.) of 114 g of amixture of 100 g of the colour-former solution of Example 1(b) and 14 gof diethyl tolylene diamine. The rotational speed is then increased to9000 r.p.m. for 45 seconds. A fine oil-in-water emulsion is formed. Therotational speed is reduced to 950 r.p.m. for 15 seconds and 153 g of a,clear solution (20° C.) of 125 g of protective colloid solution, 25 g ofpowder-form sodium bisulphite adduct of biuretised hexamethylenediisocyanate and 3 g of powder-form sodium bisulphite adduct ofhexamethylene diisocyanate are added. After a second emulsificationphase lasting 45 seconds (with the mixing siren rotating at 9000r.p.m.), the slurry is transferred to a laboratory stirrer and stirredfor a total of 120 minutes at 700 r.p.m. accompanied by heating to 50°C.

An agglomerate-free slurry containing round, transparent capsules from 1to 10 μm in diameter is obtained. High-quality CB-copying papers may beobtained by wet coating in the same way as in Example 2(a).

EXAMPLE 5

The procedure is as in Example 4 up to formation of the oil-in-wateremulsion. After reduction of the rotational speed to 950 r.p.m., 155 gof a solution of 125 g of protective colloid solution and 30 g ofpowder-form sodium bisulphite adduct of biuretised hexamethylenediisocyanate are added. After another emulsification phase lasting 45seconds (with the mixing siren rotating at 9000 r.p.m.), the slurry istransferred to a laboratory stirrer and stirred for a total of 300minutes at 700 r.p.m. while heating to 70° C. An agglomerate-free slurrycontaining round, transparent capsules from 1 to 10 μm in diameter isformed. High-quality CB copying papers may be produced by wet coating inthe same way as in Example 2(a).

EXAMPLE 6

250 g of a protective colloid solution corresponding to Example 1(a) areintroduced into a glass beaker at 80° C., followed by the addition withstirring (Kotthoff mixing siren, 950 r.p.m.) of 113.5 g of a solutionheated to 80° C. of 100 g of the colour-former solution of Example 1(b)and 13.5 g of diphenyl methane diamine. The rotational speed is thenincreased to 9000 r.p.m. for 45 seconds, resulting in the formation ofan oil-in-water emulsion. The rotational speed is then reduced to 950r.p.m. for 15 seconds and 144 g of a clear solution heated to 80° C. of125 g of protective colloid solution and 19 g of powder-form sodiumbisulphite adduct of hexamethylene diisocyanate are added. After asecond emulsification phase lasting 45 seconds (with the mixing sirenrotating 9000 r.p.m.), the slurry is transferred to a laboratory stirrerand stirred for a total of 150 minutes at 80° C. An agglomerate-freeslurry containing round, opaque capsules from 3 to 60 μm in diameter isobtained. A coating blend is prepared by mixing 1 part by wt. of slurrywith 3 parts by wt. of a 2% polyvinyl alcohol solution (Mowiol 26/88, aproduct of Hoechst AG, Frankfurt). CB-copying papers may be produced asin Example 2(a) by wet coating using a 50 μm coating knife.

EXAMPLE 7

270 g of a protective colloid solution corresponding to Example 1(a) areintroduced into a glass beaker at room temperature, followed by theaddition with stirring (Kotthoff mixing siren, 950 r.p.m.) of 64.5 g ofa mixture of 55 g of the colour-former solution of Example 1(c) and 9.5g of diethyl tolylene diamine. The rotational speed is then increased to9000 r.p.m. for 45 seconds, resulting in the formation of a very fineoil-in-water emulsion. The rotational speed is reduced to 950 r.p.m. for15 seconds and 200 g of a clear solution at room temperature of 180 g ofprotective colloid solution and 20 g of powder-form sodium bisulphiteadduct of hexamethylene diisocyanate are added. After a secondemulsification phase lasting 45 seconds (with the mixing siren rotatingat 9000 r.p.m.), the slurry is transferred to a three-necked flaskequipped with a laboratory stirrer and reflux condenser and stirred fora total of 180 minutes while heating to 90° C. and then for another 120minutes while cooling to room temperature.

An agglomerate-free slurry containing round, slightly opaque capsulesranging from 3 to 14 μm in diameter is obtained. High-quality CB copyingpapers may be produced by wet coating in the same way as in Example2(a). A dark-green impression is obtained on the CF receiving paper. Thecopying properties of the paper were equally good after one month.

A capsule powder obtained by spray drying consists of round capsuleshaving a wrinkled surface and diameters of from 3 to 11 μm. About halfthe capsules have agglomerated into clusters up to 18 μm in diameter.

Redispersion of the powder in a 2% polyvinyl alcohol solution (15 partsby wt. of powder to 85 parts by wt. of solution) gives a coating blendwith which high quality CB copying papers leaving a dark greenimpression may be obtained by wet coating in the same way as in Example2(a).

EXAMPLE 7(a)

15 minutes before the beginning of the test, a clear solution isprepared by mixing 88 parts by wt. of the colour-former solution ofExample 1(c) and 22 parts by wt. of oxadiazine trione of hexamethylenediisocyanate at 80° C., followed by cooling to room temperature.

250 g of a protective colloid solution corresponding to Example 1(a) areintroduced into a glass beaker at room temperature and 71 g of the clearsolution prepared beforehand are added with stirring (Kotthoff mixingsiren, 950 r.p.m.). After an emulsification time of 1 minute, theemulsion is transferred to a laboratory stirrer and stirred for a totalof 180 minutes at 500 r.p.m.; 2 minutes after the beginning of the test,a solution of 150 g of water and 26.4 g of diethylene triamine is added.Sufficiently stable capsules have formed after another 8 minutes sothat, 10 minutes after the beginning of the test, some of the slurry maybe knife-coated as in Example 2(a) onto a sheet of typing paper anddried without capsules being destroyed. A CB-paper is obtained which,when written on about 30 minutes after the beginning of the test,produces an olive-green impression on CF-receiving paper.

When the CB-paper is written on about 60 minutes after the beginning ofthe test, the impression obtained is barely visible. 180 minutes afterthe beginning of the test, the CB-copying paper has lost itscopyability.

CB-papers produced with slurry removed 60 minutes and 120 minutes afterthe beginning of the test produced faint copies from the outset, leavingno impression whatever after 2 hours.

The slurry obtained at the end of the test is free from agglomerates.The capsules have a liquid filling, a wrinkled surface and diameters offrom 2 to 28 μm.

EXAMPLE 8

270 g of a protective colloid solution corresponding to Example 1(a) areintroduced into a glass beaker at room temperature, followed by theaddition with stirring (Kotthoff mixing siren, 950 r.p.m.) of 64.5 g ofa mixture of 55 g of DAB 7 paraffin oil (boiling range above 360° C.)and 9.5 g of diethyl tolylene diamine. The rotational speed is thenincreased to 9000 r.p.m. for 45 seconds, resulting in the formation of afine oil-in-water emulsion. The rotational speed is reduced to 950r.p.m. for 15 seconds and 200 g of a clear solution at room temperatureof 180 g of protective colloid solution and 20 g of a powder-form sodiumbisulphite adduct of hexamethylene diisocyanate are added. After asecond emulsification phase lasting 45 seconds (with the mixing sirenrotating at 9000 r.p.m.), the slurry is transferred to a three-neckedflask equipped with a laboratory stirrer and reflux condenser andstirred for a total of 180 minutes while heating to 90° C. and then foranother 120 minutes while cooling to room temperature. The slurryobtained contains capsules ranging from 3.5 to 31 μm in diameter andloose agglomerates of these capsules. The capsules may readily beconverted into powder form by spray drying.

EXAMPLE 8(a)

To prepare an isocyanate-containing organic phase, 88 parts of DAB 7paraffin oil (boiling range above 360° C.) and 22 parts of hexamethylenediisocyanate are stirred for 5 minutes (Kotthoff mixing siren, 9000r.p.m.) at 80° C. and cooled to room temperature, resulting in theformation of a substantially unstable emulsion, rather than a solution,of the diisocyanate in the paraffin oil.

250 g of a protective colloid solution corresponding to Example 1(a) areintroduced into a glass beaker at room temperature and 71 g of theorganic emulsion prepared beforehand are added while stirring at 950r.p.m. (mixing siren). After an emulsification time of 1 minute, theoil-in-water emulsion is transferred to a laboratory stirrer (500r.p.m.). 2 minutes after the beginning of the test, a solution of 150 gof water and 64.4 g of diethylene triamine is added, resulting in theformation of a mixture of solid polyurethane urea beads and fragments inaddition to non-encapsulated paraffin oil droplets. DAB 7 paraffin oilcannot be encapsulated in this way.

EXAMPLE 8(b)

The procedure is as in Example 8(a), except that, instead ofhexamethylene diisocyanate, the oxadiazine trione of hexamethylenediisocyanate, is used and, accordingly, only 26.4 g of diethylenetriamine are added. The result obtained is the same as in Example 8(a).

EXAMPLE 9

270 g of a protective colloid solution corresponding to Example 1(a) areintroduced at room temperature into a glass beaker, followed by theaddition with stirring (Kotthoff mixing siren, 950 r.p.m.) of 64.5 g ofa mixture of 55 g of a partially hydrogenated terphenyl (Santosol 340, aproduct of the Monsanto Company) and isohexadecane in a ratio of 1:1 and9.5 g of diethyl tolylene diamine. The rotational speed is thenincreased to 9000 r.p.m. for 45 seconds, resulting in the formation of afine oil-in-water emulsion. The rotational speed is reduced to 950r.p.m. for 15 seconds and 200 g of a clear solution at 20° C. of 180 gof protective colloid solution and 20 g of a powder-form sodiumbisulphite adduct of hexamethylene diisocyanate are added. After asecond emulsification phase lasting 45 seconds (with the mixing sirenrotating at 9000 r.p.m.), the slurry is transferred to a three-neckedflask equipped with a laboratory stirrer and reflux condenser andstirred for a total of 180 minutes while heating to 90° C. and then foranother 120 minutes while cooling to room temperature. The slurryobtained contains round, transparent capsules ranging from 1.4 to 12 μmin diameter, approximately 30% of which form agglomerates up to 200 μmin size.

EXAMPLE 9(a)

To prepare an isocyanate-containing organic phase, 88 parts by wt. of amixture of a partially hydrogenated terphenyl (Santosol 340, a productof the Monsanto Company) and isohexadecane in a ratio of 1:l by wt. and22 parts by wt. of the oxadiazine trione of hexamethylene diisocyanateare stirred for 5 minutes (Kotthoff mixing siren, 9000 r.p.m.) at 80°C., followed by cooling to room temperature. A substantially unstableemulsion, rather than a solution, of the diisocyanate in the solventmixture is formed.

250 g of a protective colloid solution corresponding to Example 1(a) areintroduced at room temperature into a glass beaker, followed by theaddition with stirring (mixing siren, 950 r.p.m.) of 71 g of theemulsion prepared beforehand. After an emulsification time of 1 minute,the oil-in-water emulsion is transferred to a laboratory stirrerrotating at 500 r.p.m. 2 minutes after the beginning of the test, asolution of 150 g of water and 26.4 g of diethylene triamine is added,resulting in the formation of a mixture of solid polyurethane urea beadsin addition to non-encapsulated solvent droplets and also relativelylarge, irregular agglomerates which also contain inclusions of solvent.Encapsulation of the solvent mixture of partially hydrogenated terphenyland isohexadecane in a ratio of 1:1 by wt. is not possible by thisprocess.

EXAMPLE 10

270 g of a protective colloid solution corresponding to Example 1(a) areintroduced at room temperature into a glass beaker, followed by theaddition with stirring (Kotthoff mixing siren, 950 r.p.m.) of 63.2 g ofa mixture of 55 g of a partially hydrogenated terphenyl (Santosol 340, aproduct of the Monsanto company) and isohexadecane in a ratio of 1:1 bywt. and 8.2 g of diethyl tolylene diamine. Thereafter, the rotationalspeed is increased to 9000 r.p.m. for 45 seconds, resulting in theformation of an oil-in-water emulsion. The rotational speed is thenreduced to 950 r.p.m. for 15 seconds, followed by the addition of 229.5g of a clear solution (20° C.) of 180 g of protective colloid solutionand 49.5 g of a 40% aqueous solution of the sodium bisulphite adduct ofisophorone diisocyanate. After a second emulsification phase lasting 45seconds (with the mixing siren rotating at 9000 r.p.m.), the slurry istransferred to a three-necked flask equipped with a laboratory stirrerand reflux condenser and stirred for a total of 180 minutes whileheating to 90° C. and then for another 120 minutes while cooling to roomtemperature. The agglomerate-free slurry obtained contains capsulesranging widely in diameter from 1.4 to 150 μm. Some of the capsules arenon-spherical and opaque, but all have a liquid core.

EXAMPLE 11

270 g of a protective colloid solution corresponding to Example 1(a) areintroduced at room temperature into a glass beaker, followed by theaddition with stirring (Kotthoff mixing siren, 950 r.p.m.) of 64.5 g ofa mixture of 55 g of dodecyl benzene (Marlican S, a product of the Hulscompany, Marl) and 9.5 g of diethyl tolylene diamine. The rotationalspeed is then increased to 9000 r.p.m. for 45 seconds, resulting in theformation of a fine oil-in-water emulsion. The rotational speed isreduced to 950 r.p.m. for 15 seconds, followed by the addition of 200 gof a clear solution (20° C.) of 180 g of protective colloid solution and20 g of a powder-form sodium bisulphite adduct of hexamethylenediisocyanate. After a second emulsification phase lasting 45 seconds(with the mixing siren rotating at 9000 r.p.m.), the slurry istransferred to a three-necked flask equipped with a laboratory stirrerand reflux condenser and stirred for a total of 180 minutes whileheating to 90° C. and then for another 120 minutes while cooling to roomtemperature. The slurry obtained contains round, transparent capsulesranging from 1 to 7 μm in diameter. Approximately 30% of the capsulesform agglomerates up to 230 μm in size.

EXAMPLE 11(a)

To prepare an isocyanate-containing organic phase, 88 parts of dodecylbenzene and 22 parts by wt. of the oxadiazine trione of hexamethylenediisocyanate are stirred for 5 minutes (Kotthoff mixing siren, 9000r.p.m.) at 80° C., followed by cooling to room temperature. Asubstantially unstable emulsion, rather than a solution, of thediisocyanate in the solvent is formed.

250 g of a protective colloid solution corresponding to Example 1(a) areintroduced at room temperature into a glass beaker, followed by theaddition with stirring (mixing siren, 950 r.p.m.) of 71 g of the organicemulsion prepared beforehand. After an emulsification time of 1 minute,the oil-in-water emulsion is transferred to a laboratory stirrerrotating at 500 r.p.m. 2 minutes after the beginning of the test, asolution of 150 g of water and 26.4 g of diethylene triamine is added,resulting in the formation of a mixture of solid polyurethane urea beadsand fragments, some of which have clustered together to form relativelylarge agglomerates, in addition to non-encapsulated solvent droplets.Dodecyl benzene cannot be encapsulated by this process.

EXAMPLE 12

125 g of a protective colloid solution corresponding to Example 1(a) areintroduced at room temperature into a glass beaker, followed by theaddition with stirring (Kotthoff mixing siren, 950 r.p.m.) of 15.4 g ofa clear solution of 13.2 g of the colour-former solution of Example 1(c)and 2.2 g of diethyl tolylene diamine. The rotational speed is thenincreased to 9000 r.p.m. for 45 seconds, resulting in the formation ofan oil-in-water emulsion. The rotational speed is reduced to 950 r.p.m.for 30 seconds, followed by the addition of 100 g of a clear solution,prepared at room temperature about 15 minutes before the beginning ofthe test, of 90 g of protective colloid solution and 10 g of apowder-form sodium bisulphite adduct of an isomer mixture of tolylenediisocyanate (80% of 2,4-TDI and 20% of 2,6-TDI). After a secondemulsification phase lasting 60 seconds (with the mixing siren rotatingat 9000 r.p.m.), the slurry is transferred to a laboratory stirrer andstirred for a total of 180 minutes at 700 r.p.m. while heating to 50° C.An agglomerate-free slurry is obtained which contains transparentcapsules having a wrinkled surface and diameters of from 1 to 15 μm.

High-quality CB-copying papers may be produced as in Example 2(a) by wetcoating using a 40 μm coating knife. A dark-green impression is obtainedon the CF-receiving paper. Copyability was still as good after 1 month.

EXAMPLE 12(a)

15 minutes before the beginning of the test, a clear solution isprepared by mixing 81 parts by wt. of the colour-former solution ofExample 1(c) and 19 parts by wt. of an isomer mixture of tolylenediisocyanate (80% of 2,4-TDI and 20% of 2,6-TDI) at 80° C. and coolingthe resulting mixture to room temperature. 135 g of a protective colloidsolution corresponding to Example 1(a) are introduced at roomtemperature into a glass beaker, followed by the addition with stirring(Kotthoff mixing siren, 950 r.p.m.) of 34.1 g of the solution preparedbeforehand. The rotational speed is increased to 9000 r.p.m. and, afteran emulsification time of 45 seconds, the emulsion is transferred to alaboratory stirrer rotating at 500 r.p.m. 30 seconds later, a clearsolution of 87 g of water and 13 g of diethylene triamine is added,followed by stirring for a total of 120 minutes. An agglomerate-freeslurry is obtained, containing transparent capsules having a wrinkledsurface and diameters of from 1 to 14 μm.

When written on, a CB-paper, produced by wet coating as in Example 2(a),produces a red impression on a CF-receiving paper. The colour-former hasclearly undergone a significant chemical change as a result of reactionwith the diisocyanate. 24 hours after preparation of the slurry, thecapsules have lost their copying power both on the CB-paper prepared andin the slurry itself.

EXAMPLE 13

270 g of a protective colloid solution corresponding to Example 1(a) areintroduced at 70° C. into a glass beaker, followed by the addition withstirring (laboratory stirrer, 500 r.p.m.) of 71 g of a mixture of 11 gof diethanolamine, 30 g of Marlican S and 30 g of diethyl tolylenediamine. A very fine oil-in-water emulsion is formed. 25 seconds afteraddition of the amine mixture, 200 g of a clear solution heated to 70°C. of 180 g of protective colloid solution and 20 g of a powder-formbisulphite adduct of hexamethylene diisocyanate are added.

Formation of the capsule wall takes place very quickly, i.e. in aslittle as 10 minutes. This is reflected in thickening of the slurry. Theslurry is stirred for a total of 40 minutes at an increased rotationalspeed of 700 r.p.m. and at a temperature of 70° C. An agglomerate-freeslurry is formed, containing spherical opaque capsules having a roughwrinkled surface and ranging from 1 to 11 μm in diameter. The capsulescontain a mixture of solvent and amines.

EXAMPLE 14

A protective colloid solution is prepared by stirring 5 parts by wt. ofpolyvinyl alcohol (Mowiol 26,88, a product of Hoechst AG, Frankfurt), 10parts by wt. of xanthan (Kelzan D, a product of the Kelco Division ofBaltimore Aircoil/Chemviron SA) and 1985 parts by wt. of distilled waterat room temperature.

270 g of the protective colloid solution are introduced at 70° C. into aglass beaker, followed by the addition with stirring at 500 r.p.m.(laboratory stirrer, 6 blades, 3 cm long, 1 cm wide) of 30 g of diethyltolylene diamine. A fine oil-in-water emulsion is formed.

30 Seconds after addition of the diamine, 200 g of a clear solutionheated to 70° C. of 180 g of protective colloid solution and 20 g of apowder-form potassium bisulphite adduct of hexamethylene diisocyanateare added. The rotational speed is then increased to 700 r.p.m.,followed by stirring for a total of 70 minutes at 70° C. Thereafter,spherical, smooth transparent capsules ranging from 3 to 18 μm indiameter have formed. The slurry is completely free from agglomerates.

After cooling to room temperature, the slurry is dried in theconventional way in a laboratory spray dryer (a Mini Spray Dryer asmanufactured by the Buchi company of CH-9230 Flawil, Switzerland). Afinely divided, agglomerate-free pale yellow capsule powder is obtained.The capsules have the same diameter distribution as in the slurry, arespherical, but now have a rough surface and are opaque.

EXAMPLE 15

The procedure is initially as in Example 14 up to addition of thediethyl tolylene diamine.

30 seconds after addition of the diamine, 122.5 g of a clear solutionheated to 70° C. of 180 g of protective colloid solution and 12.5 g ofpowder-form sodium bisulphite adduct of the biuretised hexamethylenediisocyanate are added. The rotational speed is then increased to 700r.p.m., followed by stirring for a total of 70 minutes at 70° C.Spherical, opaque capsules having a rough surface and diameters of from4 to 28 μm are formed. Spray drying under the same conditions as inExample 14 gives a fine free-flowing capsule powder containing someagglomerated capsules.

EXAMPLE 16

A fine emulsion of diethyl tolylene diamine in protective colloidsolution is prepared in the same way as in Example 14. 30 seconds afteraddition of the diamine, 200 g of a clear solution of 180 g ofprotective colloid solution and 20 g of powder-form sodium bisulphiteadduct of hexamethylene diisocyanate are added.

The rotational speed is then increased to 700 r.p.m. and maintained fora total of 70 minutes.

An agglomerate-free slurry is obtained, containing spherical, smoothtransparent capsules ranging from 5 to 18 μm in diameter. The slurry maybe spray dried in the same way as in Example 14, resulting in theformation of a very fine, slightly agglomerated capsule powder.

EXAMPLE 17

A fine oil-in-water emulsion of diethyl tolylene diamine in protectivecolloid solution is prepared in the same way as in Example 14. 30seconds after addition of the diamine, 247.5 g of a clear solutionheated to 65° C. of 180 g of protective colloid solution and 67.5 g of a40% aqueous solution of the sodium bisulphite adduct of the trimer ofhexamethylene diisocyanate (calculated masked NCO-content 7.8%) areadded. The rotational speed is then increased to 700 r.p.m., thetemperature increased to 70° C. and the emulsion stirred for a total of70 minutes.

An agglomerate-free non-sedimenting slurry is formed, containing roundcapsules having a rough surface and ranging from 2.5 to 20 μm indiameter.

EXAMPLE 18

810 g of a protective colloid solution of the type used in Example 14are introduced at 70° C. into a glass beaker, followed by the additionwith stirring at 700 r.p.m. (laboratory stirrer, 6 blades, 3 m long and1 cm wide) of 90 g of diethyl tolylene diamine. A fine oil-in-wateremulsion is formed. 1 minute after addition of the diamine, 707 g of aclear solution heated to 65° C. of 540 g of protective colloid solutionand 167 g of a 40% aqueous solution of the sodium bisulphite adduct ofisophorone diisocyanate are added. After 3 minutes, the glass beaker istransferred to a Kotthoff mixing siren (type DE 032 S) and emulsifiedfor 2 minutes at 5320 r.p.m. The emulsion is then stirred for another 65minutes at 700 r.p.m. (same laboratory stirrer) accompanied by heatingto 70° C. An agglomerate-free non-sedimenting slurry is obtained,containing spherical transparent capsules having a smooth surface andranging from 1 to 17 μm in diameter.

An agglomerate-free capsule powder may be produced by spray drying. Thecapsules of the powder are spherical, opaque and have a wrinkledsurface.

EXAMPLE 19

25 parts by weight of biuretised hexamethylene diisocyanate (Desmodur®N,a product of Bayer AG) are mixed with 28 parts by weight of the capsulesof Example 5 to form a paste which is then heated to 120° C. over aperiod of 10 minutes. The mass begins to solidify at temperatures above70° C. and, on reaching 120° C., is brittle and hard.

A sample of the same polyisocyanate without capsules heated in the sameway remains liquid.

A hermetically sealed sample of the above-describedpolyisocyanate-capsule mixture retains its paste-like consistency for atleast 8 days at room temperature.

EXAMPLE 20

100 parts by weight of a chlorobenzene solution containing 25% ofbiuretised hexamethylene diisocyanate are mixed with 28 parts by weightof capsules of Example 5 and the resulting mixture heated to 120° C.over a period of 10 minutes, during which the mass hardens to form animpact-resistant solid.

A hermetically sealed comparison sample of the above-described mixtureremains liquid for at least 8 days at room temperature.

EXAMPLE 21

A fine emulsion of diethyl tolylene diamine in protective colloidsolution is prepared in the same way as in Example 14.

30 seconds after addition of the diamine, 245 g of a clear solutionheated to 65° C. of 180 g of protective colloid solution and 65 g of a40% aqueous solution of the sodium bisulphite adduct of a mixture of 41parts of isophorone diisocyanate and 59 parts of biuretisedhexamethylene diisocyanate are added. The rotational speed is thenincreased to 700 r.p.m., the temperature increased to 70° C. and theemulsion stirred for a total of 70 minutes. An agglomerate-freenon-sedimenting slurry is obtained. The capsules are spherical, have asmooth surface, are partly opaque and have diameters of from 1.5 to 15μm.

EXAMPLE 22

A fine emulsion of diethyl tolylene diamine in protective colloidsolution is prepared in the same way as in Example 18. 1 minute afteraddition of the diamine, 617 g of a clear solution heated to 65° C. of540 g of protective colloid solution, 30 g of powder-form sodiumbisulphite adduct of hexamethylene diisocyanate and 47 g of a 40%aqueous solution of the sodium bisulphite adduct of biuretisedhexamethylene diisocyanate are added. After 3 minutes, the glass beakerwas transferred to a Kotthoff mixing siren (type De 032 S) andemulsified for 2 minutes at 5320 r.p.m. The emulsion was then stirredfor another 65 minutes at 700 r.p.m. (using the same laboratory stirrer)accompanied by heating to 70° C.

An agglomerate-free, non-sedimenting slurry containing capsules rangingfrom 1 to 16 μm in diameter is obtained. The capsules are predominantlysmooth, transparent and spherical, the larger capsules are irregular inshape, opaque and have a wrinkled surface.

A spray-dried capsule powder shows good free-flow properties andcontains liquid-filled capsules which are irregular in shape, opaque andhave a wrinkled surface, and also agglomerates up to 75 μm in size.

EXAMPLE 23

15 minutes before the reaction, a clear solution of 25 parts by weightof the protective colloid solution used in Example 14 is prepared atroom temperature (approx. 23° C.) by the additon with stirring for 5minutes of 3 parts by weight of a powder-form sodium bisulphite adductof an isomer mixture of tolylene diisocyanate (80% of 2,4-TDI and 20% of2,6-TDI).

135 g of the previously used protective colloid solution are introducedat room temperature into a glass beaker, followed by the addition withstirring at 500 r.p.m. (laboratory stirrer) of 15 g of diethyl tolylenediamine. A fine oil-in-water emulsion is formed.

30 seconds after addition of the diamine, 100.0 g of the previouslyprepared solution of the bisulphite adduct are added. The rotationalspeed is then increased to 700 r.p.m. and maintained for a total of 70minutes. Throughout the duration of the test, emulsions and slurryremain at room temperature.

An agglomerate-free slurry is formed. The capsules are spherical andtransparent with a slightly wrinkled surface and have diameters of from1 to 10 μm.

A capsule powder with slight local agglomerations may be produced byspray drying. The capsules are now opaque with a much more wrinkledsurface and have a liquid core.

EXAMPLE 24

270 g of the protective colloid solution corresponding to Example 1(a)are introduced at 80° C. into a glass beaker, followed by the additionwith stirring at 700 r.p.m. (laboratory stirrer) of 20 g of a liquiddiamine mixture of 10.5 g of 4,4'-diaminodiphenyl-methane and 9.5 g ofdiethyl tolylene diamine heated to 80° C.

25 seconds after addition of the diamine mixture, 200 g of a clearsolution heated to 80° C. of 180 g of protective colloid solution and 20g of a powder-form sodium bisulphite adduct of hexamethylenediisocyanate are added.

The mixture is stirred for a total of 70 minutes at 700 r.p.m. and at80° C.

After cooling to room temperature, a slurry is obtained in whichapproximately 10% of the capsules have formed agglomerates up to 35 μmin size. The individual capsules appear partly clear and partly opaquewith a wrinkled to furrowed surface and have a solid core.

EXAMPLE 25

135 g of a protective colloid solution corresponding to Example 1(a) areintroduced at 70° C. into a glass beaker, followed by the addition withstirring at 500 r.p.m. (laboratory stirrer) of 15 g ofdiaminomethylated-cyclododecane which is liquid at room temperature. Avery fine oil-in-water emulsion is formed.

25 seconds after addition of the diamine, 112.5 g of a clear solutionheated to 70° C. of 90 g of protective colloid solution and 22.5 g of a40% aqueous solution of the sodium bisulphite adduct of isophoronediisocyanate are added.

The slurry is stirred for a total of 70 minutes at 500 r.p.m. and at 70°C. The slurry formed contains very small capsules ranging from 1 to 3 μmin diameter which have largely agglomerated into small clusters lessthan 10 μm in diameter.

EXAMPLE 26

270 g of a protective colloid solution of the type described in Example1(a) are introduced at 75° C. into a glass beaker, followed by theaddition with stirring at 500 r.p.m. (laboratory stirrer) of 30 g ofdiphenyl-methane-3,3'-dithiomethyl-4,4 '-diamine which is liquid at 75°C.

25 seconds after addition of the diamine, 115 g of a clear solutionheated to 75° C. of 180 g of protective colloid solution and 15 g of apowder-form sodium bisulphite adduct of hexamethylene diisocyanate areadded. The rotational speed is increased to 700 r.p.m. and is maintainedfor a total of 120 minutes at a temperature of 75° C. Anagglomerate-free slurry containing polyamine-filled microcapsulesranging from 1 to 12 μm in diameter is formed.

EXAMPLE 27

135 g of a protective colloid solution of the type described in Example1(a) are introduced at 70° C. into a glass beaker, followed by theaddition with stirring at 500 r.p.m. (laboratory stirrer) of 15 g of apolyamine, liquid at room temperature, produced from a prepolymercontaining 14.3% of NCO-groups of hexamethylene diisocyanate anddipropylene glycol by conversion of the terminal NCO-groups byhydrolysis into amino groups (6-amino-n-hexylcarbamic acid dipropyleneglycol diester). A coarse oil-in-water emulsion is formed.

25 seconds after addition of the diamine, 102.5 g of a clear solutionheated to 70° C. of 90 g of protective colloid solution and 12.5 g of a40% aqueous solution of the sodium bisulphite adduct of isophoronediisocyanate are added.

The slurry is stirred at 500 r.p.m. for a total of 70 minutes at atemperature of 70° C.

The slurry formed contains predominantly lemon-shaped capsules having aspherical core, as known from the production of microcapsules by complexcoacervation. The capsules range from 9 to 230 μm in diameter.

EXAMPLE 28

270 g of a protective colloid solution of the type described in Example1(a) are introduced at 98° C. into a glass beaker, followed by theaddition with stirring at 500 r.p.m. (laboratory stirrer) of 30 g of apolyamine mixture heated to 98° C. ofdiphenylmethane-3,5-diethyl-3',5'-diisopropyl-4,4'-diamine,diphenylmethane-3,3',5,5'-tetraisopropyl-4,4'-diamine anddiphenylmethane-3,3',5,5'-tetraethyl-4,4'-diamine.

25 seconds after addition of the diamine, 193 g of a clear solutionheated to 98° C. of 180 g of protective colloid solution and 13 g of apowder-form sodium bisulphite adduct of hexamethylene diisocyanate areadded. The rotational speed is increased to 700 r.p.m. for 1 minute,after which the slurry is transferred to a 1 litre three-necked flaskequipped with a reflux condenser, in which the slurry is refluxed andstirred (300 r.p.m.) for 4.5 h. The slurry formed containspolyamine-filled microcapsules ranging from 1 to 13 μm in diameter.Approximately 5% of the capsules have clustered together to formagglomerates up to 24 μm in diameter.

EXAMPLE 29

10 g of the capsule powder obtained in accordance with Example 14 areintensively mixed with 190 g of a trimethylol propane-started polyether(OH-number 35) containing more than 80% of primary OH-groups. Thedispersion formed is then thoroughly mixed with 6 g of H₂ O, 2 g ofdiethanolamine, 0.5 g of diazabicyclooctane, 4 g of tris-2-chloroethylphosphate and 0.25 g of tin(II)dioctoate. After thorough mixing, 77.4 gof tolylene diisocyanate (isomer mixture: 80% of 2,4- and 20% of2,6-tolylene diisocyanate) are added with rapid stirring and thefoamable mixture poured into an open mould. After a rise time of 83seconds, an open-cell flexible foam is obtained. The foam is thenafter-treated for 1 hour at 120° C. in a drying cabinet. A highlyelastic, flexible foam having favourable mechanical properties isobtained.

We claim:
 1. A microcapsule comprising a capsule wall enclosinghydrophobic core material produced by the process comprising emulsifyingin water or in an aqueous protective colloid solution a mixture ofhydrophobic core material and a water-insoluble polyamine containing atleast two primary amino groups, adding a water-soluble polyisocyantebisulphite adduct in the form of a powder or and aqueous solution andallowing the mixture to react to completion at a temperature of from 1°to 140° C.
 2. A microcapsule as claimed in claim 1 wherein the diameterthereof is from 0.2 to 2000 μm.
 3. A microcapsule as claimed in claim 1wherein the wall constitutes from 5 to 64% by weight of the capsule. 4.A microcapsule as claimed in claim 1 wherein the core material is awater-insoluble polyamine.
 5. A microcapsule according to claim 1wherein the hydrophobic core material comprises a dye-precursor.
 6. Themicrocapsule as claimed in claim 5 wherein the dye-precursor is selectedfrom 3,3-bis-(p-dimethylaminophenyl)-phthalide,4,4'-bis-dimethylaminobenzhydrilbenzyl ether, N-halogen phenylleucolamine, N-β-naphthyl leucolamine, N-2,4,5-trichlorophenylleucolamine, N-2,4-dichlorophenyl leucolamine,rhodamine-β-anilinolactam, rhodamine-β-(p-nitroaniline)-lactam,rhodamine-β-(p-chloroaniline)-lactam,7-dimethylamino-2-methoxy-fluorane, 7-diethylamino-3-methoxyfluorane,7-diethylamino-3-chloro-fluorane,7-diethylamino-3-chloro-2-methyl-fluorane,7-diethylamino-2,4-dimethyl-fluorane,7-diethylamino-2,3-dimethyl-fluorane,7-diethylamino-(3-acetylmethylamino)-fluorane,7-diethylamino-3-methyl-fluorne, 3,7-diethylamino-fluorane,7-diethylamino-3-(dibenzylamino)-fluroane,7-diethylamino-3-(methylbenzylamino)-fluorane,7-diethylamino-3-(chloroethylmethylamino)-fluorane,7-diethylamino-3-(dichloroethylamino)-fluorane,3,3-bis-(p-dimethylaminophenyl)-6-dimethylaminophthalide,7-diethylamino-3-(diethylamino)-fluorane, N-benzoyl leucomethylane blue,o-chlorobenzoyl leucomethylene blue, p-nitrobenzoyl leucomethylene blueand 3methyl-2,2'-spiro-bis-(benzo(f)-chromene).